The synthesis and characterization of one-dimensional (1D) semiconductor quantum-confined materials are important since they have great potential to be used as building blocks for nanoscale electronic devices and other novel applications (see Reference Documents 1-9). Among the known 1D semiconductor materials, molecular wires or quantum wires (see Reference Documents 1-5) are the thinnest 1D quantum-confined materials. However, examples of such quantum wires are rare. Recently, the present inventors have elucidated the interesting quantum confinement properties of the titanate (TiO32−) quantum wires (see Reference Document 10) which are regularly placed within a titanosilicate molecular sieve called ETS-10. It shows a length-dependent quantum confinement effect even at length scales longer than 50 nm (see Reference Documents 10-13). Its estimated effective reduced mass (μz) of exciton along the quantum wire was smaller than 0.0006 me (me=rest mass of electron), which are much smaller than the reported smallest values (InSb: 0.014 me, single-walled carbon nanotube: 0.019 me) indicating much higher exciton mobility along the titanate quantum wire than those of InSb (0.014 me) and single-walled carbon nanotube (0.019 me). The nature of electronic absorption of the titanate quantum wire was oxide-to-TiIV charge transfer, or ligand-to-metal charge transfer (LMCT)(see Reference Documents 14-16). The stretching frequency of the titanate quantum wire increases as the electron density of the wire increases (see Reference Document 14).
After elucidation of such important properties of the titanate quantum wire, it will be exciting if one could elucidate the physicochemical properties of the closely related vanadate (VO32−) quantum wire. In that sense, the discovery of a vanadosilicate AM-6 by Rocha, Anderson, and coworkers in 1997 [hereinafter, referred to as “AM-6-(RA)”] was a very important event since its structure adopts that of ETS-10 with vanadate (VO32−) quantum wires replacing titanate (TiO32−) quantum wires (see Reference Document 17). However, they had to use ETS-10 crystals as seeds in order to induce ETS-10 structure onto the vanadosilicate. Accordingly, AM-6-(RA) inevitably contains ETS-10 crystals within AM-6. In this respect, AM-6-(RA) should more strictly be defined as ETS-10 core/AM-6 shell. Furthermore, Lobo, Doren, and coworkers revealed that VO32− quantum wires in AM-6-(RA) are composed of both a V4+ and a V5+ (see Reference Documents 18-20). As a result, it is intrinsically unable to elucidate the physicochemical properties of the pure VIVO32− quantum wire. Furthermore, their procedure always simultaneously produces substantial amounts of quartz. In this sense, the methods to prepare ETS-10-free, pure AM-6 have long been awaited.
Twelve years after the report of AM-6-(RA), Sacco, Jr., and the coworkers finally developed a method of synthesizing ETS-10-free, pure AM-6 (see Reference Document 21). However, the Sacco, Jr.'s group had to use tetramethylammonium ion (TMA+) as the structure directing agent. Accordingly, this AM-6 contains TMA+ ions within the channels. Herein, the AM-will be referred to as “AM-6-(S)-TMA”. The present inventors found that AM-6-(S)-TMA also contains both a V4+ and a V5+ (see below). Furthermore, the TMA+ ions are tightly encapsulated within the channels and hence completely block the silica channels. As a result, even the ion exchange of other pristine cations (Na+ and K+) with other cations is very difficult (see below), rendering them impossible to study the important physicochemical properties of the pure VIVO32− quantum wire or the pure VIV vanadosilicate molecular sieve. The Sacco, Jr.'s group removed the TMA+ ions by treating AM-6-(S)-TMA with NH3 gas for about 3 to 4 hours at about 350° C. to 400° C. This harsh condition destroys all the vanadate (VO32−) quantum wires since they are not stable at temperatures higher than about 180° C. under vacuum (see below). Hereinafter, the NH3-treated AM-6-(S)-TMA will be referred to as “AM-6-(S)—NH3”.
Thus, there have been no methods to synthesize an ideal VIV vanadosilicate AM-6 having well preserved VIVO32− quantum wires and free from ETS-10 core and channel-blocking TMA+ cations. Furthermore, the reaction periods for the synthesis of AM-6-(RA) and AM-6-(S)-TMA are usually three days or longer, and vanadyl sulfate (VOSO4) has been used as the vanadium source, which is significantly (>5 times) more expensive than vanadium pentoxide (V2O5). Therefore, the development of rapid and inexpensive synthetic methods to produce an ideal VIV AM-6 vanadosilicate will be an important contribution to the nano and nanoporous materials science as well as to catalysis.
Many theses and patent documents have been referred to and indicated as references through the whole specification. The disclosures of the theses and patent documents referred to are incorporated herein to more clearly explain standards of the technical field pertinent to the present disclosure and the content of the present disclosure.